Control of Digestion

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Control of Digestion

• By Jo and Dave

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• If organs secreted digestive enzymes constantly
  then it would clearly be wasteful.
• The nervous system and hormones control the
  release of secretions from the various regions of
  the alimentary canal and its associated glands.

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Control by the nervous system I

• The sight, smelling and chewing of food can
  trigger the secretion of saliva from the salivary
  glands. This is a reflex action, in which action
  potentials travel from sense organs, such as the
  eyes and nose, to the central nervous system,
  then along motor neurones to the salivary glands
• The part of the brain involved in the salivation
  reflex is the medulla oblongata. The nerve that
  carry the impulse here, via the spinal cord, to
  the salivary glands are part of the autonomic
  nervous system, and both parasympathetic and
  sympathetic nerves help to stimulate salivary
  secretion.

Pavlovs experiments with dogs showed that they
could be conditioned to associate hearing a bell
ringing with food, so the bell would stimulate
the reflex action of releasing saliva.
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Control by the nervous system II

• The secretion of gastric juice into the stomach
  is also partly controlled by the nervous system.
• The sight and smell of food can also stimulate
  this reflex action.
• Nerve impulses are carried to the stomach from
  the brain along the vagus nerve, which is part of
  the parasympathetic nervous system.
• The arrival of these impulses directly stimulates
  the secretion of gastric juices and also
  initiates the release of the hormone gastrin (see
  later slides)

Vagus nerve
Parasympathetic nervous system